1. Field of the Invention
The present invention relates to a neural stimulating lead including an active fixation stabilizing structure. More specifically, the present invention relates to a stimulating lead having an active fixation stabilizing structure that includes a membrane which can be extended or expanded to form a canopy formation once the stimulating lead has been correctly positioned within an epidural space in a vertebra. The canopy formation serves to fix the position of an electrode on the lead at a desired location along and against the dura of a spinal cord traversing a vertebra of the spine.
2. Description of the Prior Art
Heretofore neural stimulating leads for use in spinal cord stimulation have had a tendency to migrate after placement. The migration has a considerable effect on stimulation, no matter how miniscule the migration is. In this respect, migration of a stimulating lead often results in poor electrical contact of an electrode on the lead with the spinal cord or results in stimulation of an improper are of the spinal cord which will negate the effect required, such as stimulation of a precise area to alleviate pain.
To overcome the problems of such migration, various mechanisms and devices have been proposed. Examples of previously proposed mechanisms and devices are disclosed in the following U.S. patents:
______________________________________ U.S. PAT. NO. PATENTEE ______________________________________ 4,285,347 Hess 4,374,527 Iversen 4,419,819 Dickhudt et al 4,519,403 Dickhudt ______________________________________
The Hess U.S. Pat. No. 4,285,347 discloses a neural electrode lead with stabilizing structure. The stabilizing structure here is defined by laterally expandable loop elements.
The Iversen U.S. Pat. No. 4,374,527 discloses a body stimulation lead which includes a plurality of lobes or undulating loops in the lead body for maintaining the position of an electrode at the distal end of the lead. In one embodiment the lobes or loops are in perpendicular planes so as to provide the lead with a crankshaft-like configuration.
The Dickhudt et al. U.S. Pat. No. 4,419,819 discloses a biomedical lead with a lobed lead anchor. The anchor comprises a sleeve which is slit in a direction parallel to the axis of the lead body and when the tubing is compressed, the slit portions expand into lobes to stabilize the position of the lead electrode therein.
The Dickhudt U.S. Pat. No. 4,519,403 discloses a neural stimulating lead having an inflatable balloon which is sealed against a first side of the lead so it inflates away from the first side which is against the dura in an epidural space to urge an electrode on the first side against the dura.
Also, there is proposed in copending application Ser. No. 667,228 a neural stimulating lead with stabilizing structure including an extendible/retractable tine which is movable between a retracted position and an extended position where the tine engages a dorsal wall surface of a vertebra for anchoring the lead within an epidural space in the vertebra.
As will be described in greater detail hereinafter, the neural stimulating lead of the present invention differs from the previously proposed neural stimulating leads by providing an active fixation stabilizing structure including a membrane on one side of the lead which can be extended or expanded by an expandable material which can be actuated to swell/expand against the membrane to form a canopy which bears against a dorsal surface of a vertebra to anchor the lead within an epidural space in a vertebra and force an electrode on the other side of the lead against the dura of the spinal cord.